Does this sign placed in the area of an intersection refer only to the roadway by which it has been placed?

In the photo you are entering a junction with a dual carriageway. On the traffic island between the roadways there are signs C-9 "keep right of the sign" and B-21 "no left turn". A no-turn sign placed already within the junction applies only to the nearest roadway in front of which it stands - on the second roadway a left turn may be allowed. The answer is: yes.

The Regulation on road signs and signals says directly that signs B-21 and B-22 placed within a junction apply only to the nearest roadway in front of which they have been placed. On a dual carriageway you cross the first roadway going straight on, and you make the left turn only after the central reservation - as long as the signs at the second roadway do not prohibit it.

Legal basis: § 22 para. 1 and 3 of the Regulation on road signs and signals